JP2003-97454A discloses a variable displacement vane pump. The variable displacement vane pump includes a rotor that receives vanes, a cam ring that has an inner circumferential cam face with which tip portions of the vanes are brought into sliding contact and that swings about a support pin, and a side plate that is in sliding contact with one end side of the rotor in the axial direction. On the side plate, a suction port for guiding working fluid into pump chambers that are defined by the rotor, the cam ring, and the adjacent vanes and a discharge port for guiding the working fluid discharged from the pump chambers are formed so as to have an arc shape, respectively.
Therefore, a suction section in which the pump chamber communicates with the suction port, a discharge section in which the pump chamber communicates with the discharge port, and transition sections that are positioned between the suction port and the discharge port are formed on the side plate. In these sections, the pump chambers move into the suction section, the transition section, the discharge section, and the transition section in this order by rotation of the rotor.